The present invention relates to a security level control apparatus, and more specifically, to a security level control apparatus for controlling security levels of communications established between communication parties.
Also, the present invention relates to a network communication system, and in particular, to a network communication system constituted by a server apparatus and a client apparatus, which perform communications, the security levels of which are set.
Network services through which electronic mails are provided are commercially available by mutually connecting computers installed in a distribution manner.
However, in network systems configured for academic purposes, typically known as the Internet, proper care is not taken to network security matters. Accordingly, these network services involve various problems, for instance wiretapping, falsification, and impersonation.
Now, a description will be made of these wiretapping, falsification, and impersonation with respect to electronic mails.
The term "wiretapping" implies that a plain text, i.e., a correspondence message not yet encrypted is read during message transmission.
The term "falsification" implies that a content of an electronic mail is modified. This falsification is performed in relaying nodes when an electronic mail is delivered via a plurality of relaying nodes.
The term "impersonation" implies that when no protection is established with respect to information for specifying a mail sender, a third party (bearing offense) falsifies the information for specifying the third party to pose as an impersonator.
To solve these network problems, at least one of the following solutions is carried out as follows. For instance, a message (data) is encrypted, an electronic signature (Message Integrity Check) is used to prevent falsification, and a user (communication party) is authenticated. In such a network communication system realized in a server/client manner, the server apparatus is authenticated and/or the client apparatus is authenticated.
As to encryption techniques, the secret key cryptosystem, the public key cryptosystem, and the like are known. In the secret key cryptosystem, the encrypting operation and the decrypting operation are carried out by using the common key between the communication parties. On the other hand, in the public key encrypting system, the key system is constituted by combining the secret keys for the individual users with the public keys, and the public keys are opened to the third party, whereas the secret keys are disclosed only to the individual users. In this public key cryptosystem, a message which has been encrypted by the public key can be solved by the secret key. For instance, when a message is transmitted from "A" to "B", "A" encrypts this message by using the public key of "B", and then "B" who has received the encrypted message can decrypt this encrypted message by using the own secret key. The person who can decrypt this encrypted message is only "B" who knows the own secret key.
As to the authentication techniques, the password authentication and the electronic signature with employment of the public key cryptosystem are known.
In the above-described conventional network techniques, a plurality of security levels are produced when certain process operations are combined with each other in order to avoid the problems such as wiretapping, falsification, and impersonation with respect to the network services.
For instance, it is conceivable that a resultant security level becomes high when electronic mail is encrypted and at the same time a user of this electronic mail is authenticated, rather than only the encryption of this electronic mail. When only the security should be emphasized, it is best to combine a large number of processing operations with each other. However, in this case, the resultant workloads would be increased.
Under such a circumstance, it is a proper solution to set the security level to which importance of a communication content is reflected. Proper setting of a security level based on importance of a message is called a "policy of security".
With respect to this "policy of security", the below-mentioned problems occur in the above-described conventional techniques.
That is, as to the first problem, the communication is performed between the communication parties in accordance with only a predetermined security policy, but cannot be carried out in accordance with other security policies.
As to the second problem, the security level of the communication party (communication destination) is continuously introduced with a top priority, so that the security level cannot be determined.
The present invention has been made to solve the above-described problems, and therefore, has a first object to provide a security level control apparatus and a network communication system, capable of executing a communication between communication parties, while a security level is not previously determined.
Also, a second object of the present invention is to provide a security level control apparatus and a network communication system, capable of executing a communication while determining the own security level.